1. Field
This disclosure relates to ear pieces that shape or suppress ambient sound.
2. Description of the Related Art
Active noise suppression headphones are effective at removing unwanted background noise while listening to music, taking phone calls, or resting quietly during travel or in other noisy situations. These head phones, whether in-ear, on-ear, or over-ear, universally employ the same successful recipe: passively attenuate high frequencies with structures, then actively cancel the low frequencies with analog and/or digital electronics. However, despite their relative success, these headphones suffer from the annoying and uncomfortable problem of occlusion.
Occlusion is the blocking and enclosure of the ear drum in its own pressurized volume. When this volume is relatively small, as is the case with ear buds, it exacerbates low-frequency fluctuations caused by motion and ambient pressure changes. Additional small fluctuations in pressure emitted by the ear bud's speaker and caused by imperfections in noise cancelling algorithms may add to the unpleasant vertiginous feelings many feel with occlusion.
Occlusion also comes with significant disappointments in auditory experience. Especially, sound from one's own voice does not travel by the usual air path into the ear canal but instead is conducted through bone and flesh. The voice is somewhat muted and high frequencies are attenuated, with the net result a feeling of isolation and introversion.
A further shortcoming of the traditional occluding devices is their inability to let desired sound pass un-attenuated. Because of the large broadband passive attenuation, any sound one intentionally desires to hear must be captured with an external microphone and replayed through the internal speaker. This works, but even the best electronics fail to achieve the clarity and enjoyment provided by a simply open ear canal.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number where the element is introduced and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.